Fundamentals of the Thermal Analysis of Complex Arrangements of Underground Heat Sources

This paper introduces a new analytical method for the 3-dimensional analysis of heat sources installed underground. Such sources include primarily electric power cables and steam pipes in urban areas. For complex arrangements of the heat sources, the heat transfer and cable rating calculations require the application of numerical methods, which call for high level of expertise and are generally difficult to use. The computational algorithm presented in this paper uses a point sources approach and is an extension of the work published by the authors based on line source modeling, with the goal of simplifying the numerical calculations. The proposed approach is applicable for all heat sources, which are directly buried in a uniform or a partially dried out soil. The method is illustrated by several numerical examples. These examples are used for comparison with the existing standard approach.

Health-Monitoring Methodology for High-Temperature Steam Pipes of Power Plants Using Real-Time Displacement Data

We developed a health-monitoring methodology for high-temperature steam pipes that estimated the life prediction of creep–fatigue interaction by directly measuring the displacement of hot parts. Three different methods (boiler code, design stress, and operating stress) were used to estimate the stress of the high-temperature pipe system. As a theoretical approach, the German boiler standard code calculates the stress according to the pipe shape, while design stress, which is also called allowable stress, was determined by a function of the operating temperature. The operating stress was immediately calculated using the surrogate model, with maximum displacement measured using the 3D displacement measurement system. To achieve the surrogate model, the stress was estimated by the pipe-stress analysis under the given displacements, and the surface-response model was developed to relate the stress and displacement. We showed that those methods are efficient methods to predict the stress and are applicable in health-monitoring methodology. Finally, the creep life and the low-cycle fatigue life were investigated using the Larson–Miller parameter equation, as well as the Smith, Hirschberg, and Manson equations. Our proposed monitoring system can be used to predict the fatigue and creep life of high-temperature steam pipes in real time, and we believe that the system can be applied to actual maintenance in thermal power plants.

A Grain Size-Dependent Equation for Creep Rupture Life of Grade 91 Steel Verified Up To 233,000 Hours

Grade 91 steel is widely used as steam pipes in ultrasupercritical (USC) steam boilers. In residual creep life assessment of the pipes by calculation, one needs creep rupture life of the steel as a function of stress and temperature in a time range longer than 105 h. Four regions with different creep rupture characteristics appear in a stress versus creep rupture life diagram of the steel. Main steam pipes made of the steel are used in a long-term region with low values of stress exponent and activation energy for creep rupture life (referred to as region G in this paper). Creep rupture lives of the steel in this region vary from heat to heat depending on their prior austenite grain size. This paper proposes a grain size-dependent equation representing creep rupture life of the steel in region G. The equation is verified with creep rupture data up to 232,833 h at 600 °C. Region G is absent in some heats with a large grain size. The equation can rationalize the absence in the heats. In a stress versus creep rupture life diagram of grade 92 steel, there is the same long-term region G. In the region, a creep rupture life of each heat is dependent on its grain size as is the case in grade 91 steel. The proposed equation accords well with the creep rupture lives of the grade 92 steel in region G.

Metallurgical Examination and Life Time Assesment of High Pressure Steam Pipes of a Palm Oil Processing Plant [Penelitian Metalurgi dan Analisa Umur Layan Pipa Uap Bertekanan Tinggi pada Sebuah Pabrik Pengolahan Minyak Kelapa Sawit]

Steel pipes are commonly used for transporting high pressure steam from a steam generating unit or boiler to a steam turbine or other processing unit. This paper presents a metallurgical examination performed on HP steam pipes of a newly constructed plant for transporting high pressure steam from a boiler to a palm oil processing plant. The aim was to assure that the material integrity of the steam pipes meet the intended specification and reliability. In addition, the aim was also to determine the estimated service life of the steam pipes. The metallurgical examination was conducted by preparing a number of specimens from the as-received three pieces of HP steam pipes. Various laboratory examinations were performed including chemical analysis, metallographic examination, hardness testing and tensile testing at 300 °C. In addition, a life-time analysis was also made using an equation based on the ASME Boiler and Pressure Vessel Code (BPVC) and data obtained from the API Standard 530. Results of the metallurgical examination obtained showed that the HP steam pipes which were made of ASTM A-106 Gr. B were all in good condition, either in microstructure or mechanical property. There were no any significant defect observed, and all the three HP steam pipes were assumed being ready to place in service. Under the intended operating pressure and temperature of 70 bar(g) and 300 °C (max), respectively it can be estimated that the HP steam pipes may likely reach some design life up to 25 years or more with the corrosion rate approximately 0.2 - 0.3 mm/year. AbstrakPipa baja sering digunakan untuk menyalurkan uap bertekanan tinggi dari sebuah ketel uap menuju ke unit turbin uap atau ke unit produksi lainnya. Tulisan ini menyajikan penelitian metalurgi yang dilakukan pada sejumlah pipa uap bertekanan tinggi pada sebuah pabrik yang baru dibangun untuk menyalurkan uap bertekanan tinggi dari sebuah ketel uap menuju ke pabrik pengolahan minyak ke-lapa sawit. Tujuannya adalah untuk memastikan bahwa keterpaduan material pipa uap memiliki kesesuaian dengan spesifikasi dan kehandalan yang diinginkan. Disamping itu, tujuannya juga ada-lah untuk memperkirakan umur layan pipa uap tersebut. Pengujian metalurgi dilakukan dengan mempersiapkan sejumlah benda uji yang diambil dari tiga potongan pipa uap yang diterima, yaitu meliputi : analisa kimia, uji metalografi dan uji kekerasan serta uji tarik pada suhu 300 °C. Disamping itu, analisa umur juga dibuat menggunakan persamaan yang diambil dari ASME Boiler dan BPVC (pressure vessel code) dan dari data standar API 530. Hasil pengujian metalurgi yang diperoleh menun-jukkan bahwa pipa uap bertekanan tinggi yang dibuat dari material ASTM A-106 Gr. B seluruhnya dalam kondisi baik, baik dari segi struktur mikro maupun dari segi sifat mekanis. Hasil pengujian juga menunjukkan bahwa pada struktur mikro tidak diketemukan adanya cacat yang berarti, dan seluruh (ke tiga) pipa uap yang di uji tersebut diperkirakan dalam keadaan siap untuk dioperasikan. Pada tekanan operasi 70 bar(g) dan temperatur operasi maksimum 300 °C yang direncanakan, diperkirakan bahwa pipa uap tersebut dapat memberikan umur desain hingga 25 tahun atau lebih dengan laju korosi 0,2 - 0,3mm/tahun.

Development and Testing of a Multitransducer System for Measuring Height of Condensed Water in Steam Pipes With Steady-State and Turbulent Flow Conditions

A system consisting of a multiplexer and multiple ultrasonic probes was developed for in situ monitoring of the water condensation height in steam pipes under steady-state and turbulent flow conditions. The measurement method, the signal processing techniques, the experimental setup, and the test results are presented in this paper. The feasibility and efficiency of the developed multitransducers and signal processing algorithms were demonstrated. The measured water height and wave pattern in dynamic surface conditions inside the pipe were verified through the snapshot of the recorded video images. The developed methodology built the framework for the use of multiple transducers array ultrasonic system for practical application to in situ monitor the water height in steam pipes.